It is known to form the cross sectional profile of a tubular member by a hydro-forming process in which a fluid filled tubular blank is placed within a die and then the die is closed so that the tubular blank is pinched within the die. Fluid pressure is then increased inside the tubular member to expand the blank outwardly against the die cavity to provide a tubular product having a die formed cross sectional profile. The tubular product may have different cross sectional profiles along the length thereof.
A disadvantage of the aforedescribed method of forming a tubular member resides in the fact that the circumferential measure of the cross section must be of generally the same dimension all along the length of the tubular member. The prior art has recognized that the circumferential expansion of the blank is limited to about two to five percent when using readily available grades of tubular steel. Expansions of circumference of up to about 20 percent can be performed if the tubular blank is of fully annealed tubular steel. This limitation in the extent of permissible expansion, limits the potential for forming tubular members having differing cross sectional circumferential measure along the length of the tubular member.
It would be desirable to provide a forming method which would enable the manufacture of a tubular member which would have substantially different cross section circumferential measure along the length of the tubular member.
The aforedescribed tubular members are particularly useful in the manufacture of vehicle bodies. For example, in U.S. Pat. No. 4,945,682 it is shown that such a tubular member may be employed to reinforce a vehicle door molded of synthetic resin. In many vehicle structures, such as doors, it would be desirable to provide such a tubular member with a flange to facilitate the attachment thereto of weather strips or other vehicle body components.
Therefore it would be desirable to provide a method of forming an integral flange on a hydro-formed tubular member.